Wednesday, December 1, 2010

Mobile phone features

Mobile phones are designed to work on cellular networks and contain a standard set of services that allow phones of different types and in different countries to communicate with each other. However, they can also support other features added by various manufacturers over the years:

roaming which permits the same phone to be used in multiple countries, providing that the operators of both countries have a roaming agreement.

send and receive data and faxes (if a computer is attached), access WAP services, and provide full Internet access using technologies such as GPRS.

applications like a clock, alarm, calendar and calculator and a few games.

Sending and receiving pictures and videos through MMS, and for short distances with e.g. Bluetooth.

GPS receivers integrated or connected (i.e. using Bluetooth) to cell phones, primarily to aid in dispatching emergency responders and road tow truck services. This feature is generally referred to as E911.

Push to talk, available on some mobile phones, is a feature that allows the user to be heard only while the talk button is held, similar to a walkie-talkie.

features aimed toward personalisation, such as user defined and downloadable ring tones and logos, and interchangeable covers, which have helped in the uptake by the teenage market. Mobile phone content advertising has become massively popular but has also drawn a great deal of criticism. Usually one can choose between a ring tone, a vibrating alert, or a combination of both.

As a result of all these features packed into a tiny device, mobile phones have recently gained reputations for their poor ergonomics. Their small size, plethora of features and modes, and attempts at stylish design may make them difficult and confusing to use.

Multi-mode and multi-band mobile phones

Most mobile phone networks are digital and use the GSM, CDMA or iDEN standard which operate at various radio frequencies. A multi-mode phone operates across different standards whereas a multi-band phone (also known more specifically as dual, tri or quad band) mobile phone is a phone which is designed to work on more than one radio frequency. Some multi-mode phones can operate on analog networks as well (for example, dual band, tri-mode: AMPS 800 / CDMA 800 / CDMA 1900).

For a GSM phone, dual-band usually means 850 / 1900 MHz in the United States and Canada, 900 / 1800 MHz in Europe and most other countries. Tri-band means 850 / 1800 / 1900 MHz or 900 / 1800 / 1900 MHz. Quad-band means 850 / 900 / 1800 / 1900 MHz, also called a world phone, since it can work on any GSM network.

Multi-band phones have been valuable to enable roaming whereas multi-mode phones helped to introduce WCDMA features without customers having to give up the wide coverage of GSM. Almost every single true 3G phone sold is actually a WCDMA/GSM dual-mode mobile. This is also true of 2.75G phones such as those based on CDMA-2000 or EDGE.

Challenges in producing multi-mode phones

The special challenge involved in producing a multi-mode mobile is in finding ways to share the components between the different standards. Obviously, the phone keypad and display should be shared, otherwise it would be hard to treat as one phone. Beyond that, though, there are challenges at each level of integration. How difficult these challenges are depends on the differences between systems. When talking about IS-95/GSM multi-mode phones, for example, or AMPS/IS-95 phones, the base band processing is very different from system to system. This leads to real difficulties in component integration and so to larger phones.

An interesting special case of multi-mode phones is the WCDMA/GSM phone. The radio interfaces are very different from each other, but mobile to core network messaging has strong similarities, meaning that software sharing is quite easy. Probably more importantly, the WCDMA air interface has been designed with GSM compatibility in mind. It has a special mode of operation, known as punctured mode, in which, instead of transmitting continuously, the mobile is able to stop sending for a short period and try searching for GSM carriers in the area. This mode allows for safe inter-frequency handovers with channel measurements which can only be approximated using "pilot signals" in other CDMA based systems.

A final interesting case is that of mobiles covering the DS-WCDMA and MC-CDMA 3G variants of the CDMA-2000 protocol. Initially, the chip rate of these phones was incompatible. As part of the negotiations related to patents, it was agreed to use compatible chip rates. This should mean that, despite the fact that the air and system interfaces are quite different, even on a philosophical level, much of the hardware for each system inside a phone should be common with differences being mostly confined to software.

Data communications

Main article: Mobile Internet

Mobile phones are now heavily used for data communications such as SMS messages, browsing mobile web sites, and even streaming audio and video files. The main limiting factors are the size of the screen, lack of a keyboard, processing power and connection speed. Most cellphones, which supports data communications, can be used as wireless modems (via cable or bluetooth), to connect computer to internet. Such access method is slow and expensive, but it can be available in very remote areas.

With newer smartphones, screen resolution and processing power has become bigger and better. Some new phone CPUs run at over 1 GHz. Many complex programs are now available for the various smartphones, such as Symbian and Windows Mobile.

Connection speed is based on network support. Originally data transfers over GSM networks were possible only over CSD (circuit switched data), it has bandwidth of 9600 bit/s and usually is billed by connection time (from network point of view, it does not differ much from voice call). Later, there were introduced improved version of CSD - HSCSD (high speed CSD), it could use multiple time slots for downlink, improving speed. Maximum speed for HSCSD is ~42 kbit/s, it also is billed by time. Later was introduced GPRS (general packet radio service), which operates on completely different principle. It also can use multiple time slots for transfer, but it does not tie up radio resources, when not transferring data (as opposed to CSD and like). GPRS usually is prioritized under voice and CSD, so latencies are large and variable. Later, GPRS was upgraded to EDGE, which differs mainly by radio modulation, squeezing more data capacity in same radio bandwidth. GPRS and EDGE usually are billed by data traffic volume. Some phones also feature full Qwerty keyboards, such as the LG enV.

As of April 2006, several models, such as the Nokia 6680, support 3G communications. Such phones have access to the Web via a free download of the Opera web browser. Verizon Wireless models come with Internet Explorer pre-loaded onto the phone.

Vulnerability to Mobile viruses

Main article: Mobile virus

As more complex features are added to phones, they become more vulnerable to viruses which exploit weaknesses in these features. Even text messages can be used in attacks by worms and viruses. Advanced phones capable of e-mail can be susceptible to viruses that can multiply by sending messages through a phone's address book.

A virus may allow unauthorized users to access a phone to find passwords or corporate data stored on the device. Moreover, they can be used to commandeer the phone to make calls or send messages at the owner's expense.

Mobile phones used to have proprietary operating system unique only to the manufacturer which had the beneficial effect of making it harder to design a mass attack. However, the rise of software platforms and operating systems shared by many manufacturers such as Java, Microsoft operating systems, Linux, or Symbian OS, may increase the spread of viruses in the future.

Bluetooth is a feature now found in many higher-end phones, and the virus Caribe hijacked this function, making Bluetooth phones infect other Bluetooth phones running the Symbian OS. In early November 2004, several web sites began offering a specific piece of software promising ringtones and screensavers for certain phones. Those who downloaded the software found that it turned each icon on the phone's screen into a skull-and-crossbones and disabled their phones, so they could no longer send or receive text messages or access contact lists or calendars. The virus has since been dubbed "Skulls" by security experts. The Commwarrior-A virus was identified in March 2005, and it attempts to replicate itself through MMS to others on the phone's contact list. Like Cabir, Commwarrior-A also tries to communicate via Bluetooth wireless connections with other devices, which can eventually lead to draining the battery. The virus requires user intervention for propagation however.

Bluetooth phones are also subject to bluejacking, which although not a virus, does allow for the transmission of unwanted messages from anonymous Bluetooth users.

Cameras

Main articles: Videophone and Camera phone

Most current phones also have a built-in digital camera (see camera phone), that can have resolutions as high as 8M pixels. This gives rise to some concern about privacy, in view of possible voyeurism, for example in swimming pools. South Korea has ordered manufacturers to ensure that all new handsets emit a beep whenever a picture is taken.

Sound recording and video recording is often also possible. Most people do not walk around with a video camera, but do carry a phone. The arrival of video camera phones is transforming the availability of video to consumers, and helps fuel citizen journalism.